How many paywall sites have half decent forums/discussions? It seems like that's the sort of thing they could leverage to drive their subscriptions, kind of lik

How many paywall sites have half decent forums/discussions? It seems like that's the sort of thing they could leverage to drive their subscriptions, kind of like how the letters to the editor section used to get used. At the moment this is outsourced to twitter/facebook/reddiit/etc and they get no revenue from it.